Student engineers develop and test a hybrid power train: Part 1 - the model

Challenge X is a three-year program (now in its final year) that tests teams from 17 universities to come up with technology to reduce automotive energy consumption and emissions, and integrate their solutions into a Chevy Equinox SUV/passenger-car crossover vehicle. While previous student competitions focused on hardware mods, the current contest includes a strong modeling and simulation component, as well as subsystem development and testing. Read more about Challenge X and check out the competition's website for the latest developments.

It's 2:00 a.m. in Terre Haute, Indiana. In six hours our vehicle will be shipped to Mesa, Arizona, leaving enough time for our first (and last) parking-lot test. The hybrid 2005 Chevrolet Equinox hums across the blacktop in its all-electric mode, sounding like an over-sized golf cart, not a compact SUV. The sound of its diesel engine automatically kicking in then lets us know our prototype system actually works! Our "Warthog," so named as she sounded like a turboprop airplane, leaked oil worse than an old Jaguar, but she worked. She was result of over two years of hard work and perseverance, late nights, and long hours; she was our very own hybrid vehicle.

Our team was brand new to vehicle competitions, but we wanted to push the limits of our technologyand ourselves. This desire lead us to employ a power-split architecture, similar to the Toyota Prius. Little did we know the difficulty of actually controlling this design, let alone the challenges of building it.

However, we were able to create a computer simulation of our vehicle and develop a robust control strategy without the fear of "breaking" components thanks in part to extensive use of software tools supplied by The Mathworks.

Planning a hybrid
The Challenge X competition has college teams follow General Motor's Global Vehicle Development Process. Teams did not receive a vehicle until Year 2, while Year 1 was devoted to research and virtual design.

First year deliverables included fuel and hybrid architecture selection, in-vehicle component layout, and a vehicle control strategy. We selected B-20 Bio-Diesel as our fuel because of its low well-to-wheels emissions and high fuel economy potential. Powertrain System Analysis Toolkit (PSAT), a program based on MATLAB®, developed by Argonne National Labs, was used to compare hybrid architectures based upon a Taguchi DoE (4-8 factors at 3 levels).

Modeling and simulation were vital to the work done by the Rose-Hulman Institute of Technology Challenge X team. The simulations showed that a power-split architecture resulted in the best combination of performance times (for 0-60 mph and 50-70 mph accelerations) and the highest fuel economy (about 40 mpgge (miles per gallon gasoline equivalent)).

This power-split architecture (see below) couples a diesel internal combustion engine (ICE) with two electric machines, operable as either motors or generators through a three degree-of-freedom planetary gear-set (PGS).

The power-split architecture connects a diesel engine and two electric machines together via a three degree-of-freedom planetary gear set.

In order to avoid confusion, the ICE is called the "engine" and the motors are M1 and M2. The engine is connected via a pass-thru shaft to the planet carrier of the PGS; M2 is connected to the sun gear; and, M1 is connected to both the ring gear and the rear differential. This physical implementation, dubbed "Frankencase," relied upon modifying two 4x4 (four-wheel drive) transfer cases to house the PGS and provide connections for the electric motors. This method, while inefficient and noisy (hence the name "Warthog"), worked well enough for a proof-of-concept vehicle.